A resonant asymmetrical half-bridge flyback power converter includes: a first transistor and a second transistor switching a transformer coupled to a capacitor for generating an output power; a voltage divider coupled to an auxiliary winding of the transformer; a differential sensing circuit which includes a first terminal and a second terminal coupled to the voltage divider to sense an auxiliary signal generated by the auxiliary winding for generating a peak signal and a demagnetization-time signal; and a PWM control circuit configured to generate a first PWM signal and a second PWM signal in accordance with the peak signal and the demagnetization-time signal, for controlling the first transistor and the second transistor respectively; wherein a period of an enabling state of the demagnetization-time signal is correlated to the output power level; wherein the peak signal is related to a quasi-resonance of the transformer after the transformer is demagnetized.
Legal claims defining the scope of protection, as filed with the USPTO.
1. A switching control circuit for use in controlling a power stage circuit of a resonant asymmetrical half-bridge flyback power converter, wherein the power stage circuit includes a transformer, a resonant capacitor, a first transistor and a second transistor, which are coupled to convert an input power to an output power, the switching control circuit comprising: a voltage divider, coupled to an auxiliary winding of the transformer for dividing an auxiliary signal generated by the auxiliary winding; a differential input sensing circuit which includes a first input terminal and a second input terminal coupled to the voltage divider to sense the auxiliary signal for generating a peak signal and a demagnetization-time signal; a feedback circuit, configured to operably generate a feedback signal according to an electrical parameter of the output power of the resonant AHB flyback power converter; and a PWM control circuit, configured to operably generate a first PWM signal and a second PWM signal in accordance with the feedback signal, the peak signal and the demagnetization-time signal, for controlling a first transistor and a second transistor of the resonant AHB flyback power converter respectively; wherein the first PWM signal and the second PWM signal are configured to switch the transformer for generating the output power of the resonant AHB flyback power converter; wherein a period of an enabling state of the demagnetization-time signal is correlated to a current level or a power level of the output power of the resonant AHB flyback power converter; wherein the peak signal is related to a quasi-resonance of the transformer after the transformer is demagnetized.
2. The switching control circuit of claim 1, wherein the differential input sensing circuit generates the peak signal when the first PWM signal is turned to an off state for turning off the first transistor and the auxiliary signal is higher than a voltage threshold.
3. The switching control circuit as claimed in claim 1, further comprising a first input circuit coupled to the first input terminal for generating an input-voltage related current signal when the first PWM signal is turned to an on state for turning on the first transistor and the transformer is magnetized; in which the input-voltage related current signal is correlated to the level of an input voltage of the resonant AHB flyback power converter.
4. The switching control circuit as claimed in claim 3, wherein the differential input sensing circuit is configured to generate an output-voltage related current signal according to the voltage across the first input terminal and the second input terminal, wherein the output-voltage related current signal is correlated to the level of an output voltage of the resonant AHB flyback power converter.
5. The switching control circuit as claimed in claim 4, wherein the output-voltage related current signal is configured to generate a reflected output-voltage signal for the over-voltage protection and the under-voltage protection of the output voltage of the resonant AHB flyback power converter.
6. The switching control circuit as claimed in claim 4, wherein the demagnetization-time signal is generated according to the output-voltage related current signal, the input-voltage related current signal and an on-time of the first PWM signal.
7. The switching control circuit as claimed in claim 1, further comprising a timing emulation circuit; wherein the demagnetization-time signal is turned to the enabling state when the first PWM signal is turned to an off state for turning off the first transistor; and the demagnetization-time signal is turned to an disabled state when a capacitor of the timing emulation circuit is discharged lower than a first discharge-threshold; wherein the capacitor of the timing emulation circuit is charged by the input-voltage related current signal during the on-time of the first PWM signal, and is discharged by the output-voltage related current signal after the first PWM signal is turned the off state.
8. The switching control circuit as claimed in claim 7, wherein a boundary extension signal is generated when the voltage of the capacitor is lower than a second discharge-threshold to continue the period of the demagnetization-time signal to generate a backward circulated-current for achieving zero-voltage switching of the first transistor.
9. The switching control circuit as claimed in claim 1, wherein an off-time period of the first PWM signal is related to the level of the feedback signal; wherein the off-time period of the first PWM signal is increased in response to the decrease of the output load of the resonant AHB flyback power converter.
10. The switching control circuit as claimed in claim 1, wherein an on-time period of the second PWM signal is longer than the demagnetizing time period of the transformer for achieving a zero-voltage switching of the resonant AHB flyback power converter.
11. The switching control circuit as claimed in claim 1, wherein an output voltage of the resonant AHB flyback power converter is programmable and includes a maximum value and a minimum value, wherein a ratio between the maximum value and the minimum value is equal to or higher than 4, or is equal to or higher than 9.
12. The switching control circuit as claimed in claim 1, wherein the resonant AHB flyback power converter is an USB PD power converter, wherein a maximum value of the output voltage is 48V and a minimum value of the output voltage is 5V.
13. A resonant asymmetrical half-bridge flyback power converter, comprising: a power stage circuit, including a transformer, a resonant capacitor, a first transistor and a second transistor, which are coupled to convert an input power to an output power; and a switching control circuit configured to control the power stage circuit of the resonant AHB flyback power converter-, including: a voltage divider, coupled to an auxiliary winding of the transformer for dividing an auxiliary signal generated by the auxiliary winding; a differential input sensing circuit which includes a first input terminal and a second input terminal coupled to the voltage divider to sense the auxiliary signal for generating a peak signal and a demagnetization-time signal; a feedback circuit, configured to operably generate a feedback signal according to an electrical parameter of the output power of the resonant AHB flyback power converter; and a PWM control circuit, configured to operably generate a first PWM signal and a second PWM signal in accordance with the feedback signal, the peak signal and the demagnetization-time signal, for controlling a first transistor and a second transistor of the resonant AHB flyback power converter respectively; wherein the first PWM signal and the second PWM signal are configured to switch the transformer for generating the output power of the resonant AHB flyback power converter; wherein a period of an enabling state of the demagnetization-time signal is correlated to a current level or a power level of the output power of the resonant AHB flyback power converter; wherein the peak signal is related to a quasi-resonance of the transformer after the transformer is demagnetized.
14. The resonant AHB flyback power converter of claim 13, wherein the differential input sensing circuit generates the peak signal when the first PWM signal is turned to an off state for turning off the first transistor and the auxiliary signal is higher than a voltage threshold.
15. The resonant AHB flyback power converter of claim 13, wherein the switching control circuit further including a first input circuit coupled to the first input terminal for generating an input-voltage related current signal when the first PWM signal is turned to an on state for turning on the first transistor and the transformer is magnetized; in which the input-voltage related current signal is correlated to the level of an input voltage of the resonant AHB flyback power converter.
16. The resonant AHB flyback power converter of claim 15, wherein the differential input sensing circuit is configured to generate an output-voltage related current signal according to the voltage across the first input terminal and the second input terminal, wherein the output-voltage related current signal is correlated to the level of an output voltage of the resonant AHB flyback power converter.
17. The resonant AHB flyback power converter of claim 16, wherein the output-voltage related current signal is configured to generate a reflected output-voltage signal for the over-voltage protection and the under-voltage protection of the output voltage of the resonant AHB flyback power converter.
18. The resonant AHB flyback power converter of claim 16, wherein the demagnetization-time signal is generated according to the output-voltage related current signal, the input-voltage related current signal and an on-time of the first PWM signal.
19. The resonant AHB flyback power converter of claim 13, wherein the switching control circuit further including a timing emulation circuit; wherein the demagnetization-time signal is turned to the enabling state when the first PWM signal is turned to an off state for turning off the first transistor; and the demagnetization-time signal is turned to an disabled state when a capacitor of the timing emulation circuit is discharged lower than a first discharge-threshold; wherein the capacitor of the timing emulation circuit is charged by the input-voltage related current signal during the on-time of the first PWM signal, and is discharged by the output-voltage related current signal after the first PWM signal is turned the off state.
20. The resonant AHB flyback power converter of claim 19, wherein a boundary extension signal is generated when the voltage of the capacitor is lower than a second discharge-threshold to continue the period of the demagnetization-time signal to generate a backward circulated-current for achieving zero-voltage switching of the first transistor.
21. The resonant AHB flyback power converter of claim 13, wherein an off-time period of the first PWM signal is related to the level of the feedback signal; wherein the off-time period of the first PWM signal is increased in response to the decrease of the output load of the resonant AHB flyback power converter.
22. The resonant AHB flyback power converter of claim 13, wherein an on-time period of the second PWM signal is longer than the demagnetizing time period of the transformer for achieving a zero-voltage switching of the resonant AHB flyback power converter.
23. The resonant AHB flyback power converter of claim 13, wherein an output voltage of the resonant AHB flyback power converter is programmable and includes a maximum value and a minimum value, wherein a ratio between the maximum value and the minimum value is equal to or higher than 4, or is equal to or higher than 9.
24. The resonant AHB flyback power converter of claim 13, wherein the resonant AHB flyback power converter is an USB PD power converter, wherein a maximum value of the output voltage is 48V and a minimum value of the output voltage is 5V.
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February 14, 2023
April 8, 2025
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